From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FD23C433E0 for ; Fri, 15 May 2020 16:16:18 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CC8062070A for ; Fri, 15 May 2020 16:16:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ebzh8CDD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC8062070A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57118 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jZd0S-0007EX-VL for qemu-devel@archiver.kernel.org; Fri, 15 May 2020 12:16:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33876) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jZczp-0006mt-JV for qemu-devel@nongnu.org; Fri, 15 May 2020 12:15:37 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:56234 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jZczn-0006Lc-9Z for qemu-devel@nongnu.org; Fri, 15 May 2020 12:15:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589559333; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=w6Dw3im+AeacAMiZvf8yC0F13GvlTYhUl8LjrRcL1a8=; b=ebzh8CDDHsQtcgrsIo82Nk4gRq3mxhLQPoXfNFMJ7HthA2tTDNzJn8Q9m86TtTrRXdZaDe 2D7XXWrwCzjDjMkEr+kbtM5t7BL4HOzgoYYZsl+DizxK+mm55NPJniEYQz9IMkIEq7iavB XP6KLVtJDkbk8xbw/0eSYiNsi/Xjr3g= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-378-kNmdEkAePo-izissdMEJ0g-1; Fri, 15 May 2020 12:15:32 -0400 X-MC-Unique: kNmdEkAePo-izissdMEJ0g-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1229F83DB37; Fri, 15 May 2020 16:15:31 +0000 (UTC) Received: from work-vm (ovpn-114-149.ams2.redhat.com [10.36.114.149]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9F91262491; Fri, 15 May 2020 16:15:23 +0000 (UTC) Date: Fri, 15 May 2020 17:15:21 +0100 From: "Dr. David Alan Gilbert" To: David Hildenbrand Subject: Re: [PATCH v1 01/17] exec: Introduce ram_block_discard_set_(unreliable|required)() Message-ID: <20200515161521.GJ2954@work-vm> References: <20200506094948.76388-1-david@redhat.com> <20200506094948.76388-2-david@redhat.com> <8dc6cefb-63ee-9310-ce18-abf558a08b39@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8dc6cefb-63ee-9310-ce18-abf558a08b39@redhat.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Received-SPF: pass client-ip=205.139.110.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/14 23:27:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , kvm@vger.kernel.org, "Michael S . Tsirkin" , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * David Hildenbrand (david@redhat.com) wrote: > On 06.05.20 11:49, David Hildenbrand wrote: > > We want to replace qemu_balloon_inhibit() by something more generic. > > Especially, we want to make sure that technologies that really rely on > > RAM block discards to work reliably to run mutual exclusive with > > technologies that break it. > > > > E.g., vfio will usually pin all guest memory, turning the virtio-balloon > > basically useless and make the VM consume more memory than reported via > > the balloon. While the balloon is special already (=> no guarantees, same > > behavior possible afer reboots and with huge pages), this will be > > different, especially, with virtio-mem. > > > > Let's implement a way such that we can make both types of technology run > > mutually exclusive. We'll convert existing balloon inhibitors in successive > > patches and add some new ones. Add the check to > > qemu_balloon_is_inhibited() for now. We might want to make > > virtio-balloon an acutal inhibitor in the future - however, that > > requires more thought to not break existing setups. > > > > Cc: "Michael S. Tsirkin" > > Cc: Richard Henderson > > Cc: Paolo Bonzini > > Signed-off-by: David Hildenbrand > > --- > > balloon.c | 3 ++- > > exec.c | 48 +++++++++++++++++++++++++++++++++++++++++++ > > include/exec/memory.h | 41 ++++++++++++++++++++++++++++++++++++ > > 3 files changed, 91 insertions(+), 1 deletion(-) > > > > diff --git a/balloon.c b/balloon.c > > index f104b42961..c49f57c27b 100644 > > --- a/balloon.c > > +++ b/balloon.c > > @@ -40,7 +40,8 @@ static int balloon_inhibit_count; > > > > bool qemu_balloon_is_inhibited(void) > > { > > - return atomic_read(&balloon_inhibit_count) > 0; > > + return atomic_read(&balloon_inhibit_count) > 0 || > > + ram_block_discard_is_broken(); > > } > > > > void qemu_balloon_inhibit(bool state) > > diff --git a/exec.c b/exec.c > > index 2874bb5088..52a6e40e99 100644 > > --- a/exec.c > > +++ b/exec.c > > @@ -4049,4 +4049,52 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root) > > } > > } > > > > +static int ram_block_discard_broken; > > + > > +int ram_block_discard_set_broken(bool state) > > +{ > > + int old; > > + > > + if (!state) { > > + atomic_dec(&ram_block_discard_broken); > > + return 0; > > + } > > + > > + do { > > + old = atomic_read(&ram_block_discard_broken); > > + if (old < 0) { > > + return -EBUSY; > > + } > > + } while (atomic_cmpxchg(&ram_block_discard_broken, old, old + 1) != old); > > + return 0; > > +} > > + > > +int ram_block_discard_set_required(bool state) > > +{ > > + int old; > > + > > + if (!state) { > > + atomic_inc(&ram_block_discard_broken); > > + return 0; > > + } > > + > > + do { > > + old = atomic_read(&ram_block_discard_broken); > > + if (old > 0) { > > + return -EBUSY; > > + } > > + } while (atomic_cmpxchg(&ram_block_discard_broken, old, old - 1) != old); > > + return 0; > > +} > > + > > +bool ram_block_discard_is_broken(void) > > +{ > > + return atomic_read(&ram_block_discard_broken) > 0; > > +} > > + > > +bool ram_block_discard_is_required(void) > > +{ > > + return atomic_read(&ram_block_discard_broken) < 0; > > +} > > + > > #endif > > diff --git a/include/exec/memory.h b/include/exec/memory.h > > index e000bd2f97..9bb5ced38d 100644 > > --- a/include/exec/memory.h > > +++ b/include/exec/memory.h > > @@ -2463,6 +2463,47 @@ static inline MemOp devend_memop(enum device_endian end) > > } > > #endif > > > > +/* > > + * Inhibit technologies that rely on discarding of parts of RAM blocks to work > > + * reliably, e.g., to manage the actual amount of memory consumed by the VM > > + * (then, the memory provided by RAM blocks might be bigger than the desired > > + * memory consumption). This *must* be set if: > > + * - Discarding parts of a RAM blocks does not result in the change being > > + * reflected in the VM and the pages getting freed. > > + * - All memory in RAM blocks is pinned or duplicated, invaldiating any previous > > + * discards blindly. > > + * - Discarding parts of a RAM blocks will result in integrity issues (e.g., > > + * encrypted VMs). > > + * Technologies that only temporarily pin the current working set of a > > + * driver are fine, because we don't expect such pages to be discarded > > + * (esp. based on guest action like balloon inflation). > > + * > > + * This is *not* to be used to protect from concurrent discards (esp., > > + * postcopy). > > + * > > + * Returns 0 if successful. Returns -EBUSY if a technology that relies on > > + * discards to work reliably is active. > > + */ > > +int ram_block_discard_set_broken(bool state); > > + > > +/* > > + * Inhibit technologies that will break discarding of pages in RAM blocks. > > + * > > + * Returns 0 if successful. Returns -EBUSY if discards are already set to > > + * broken. > > + */ > > +int ram_block_discard_set_required(bool state); > > + > > +/* > > + * Test if discarding of memory in ram blocks is broken. > > + */ > > +bool ram_block_discard_is_broken(void); > > + > > +/* > > + * Test if discarding of memory in ram blocks is required to work reliably. > > + */ > > +bool ram_block_discard_is_required(void); > > + > > #endif > > > > #endif > > > > I'm wondering if I'll just call these functions > > ram_block_discard_disable() > > and > > ram_block_discard_require() Yeh I prefer that. Dave > -- > Thanks, > > David / dhildenb -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK